Sjögren's syndrome is a systemic autoimmune disease in which immune cells attack and destroy the exocrine glands that produce saliva and tears. Sjögren's syndrome can also affect multiple organs, including kidneys and lungs. It is estimated that approximately 4 million people in the United States suffer from Sjögren's syndrome. Nine out of ten Sjögren's patients are women, with the average age of onset being in the late 40s. Sjögren's syndrome can occur in all age groups of both women and men. Sjögren's syndrome can occur independently, referred to as primary Sjögren's syndrome, or may develop years after the onset of an associated rheumatic disorder, referred to as secondary Sjögren's syndrome. The prevalence of primary Sjögren's syndrome varies from about 0.05% to 5% of the population, and the incidence of diagnosed cases has been reported to be about 4 per 100,000 people yearly (Kok et al., 2003, Ann Rhem Dis 62, 11038-1046).
Xerostomia (dry mouth) and xerophthalmia (conjunctivitis sicca, dry eyes) are hallmarks of Sjögren's syndrome (Fox et al., 1985, Lancet 1, 1432-1435) Immunologically-activated or apoptotic glandular epithelial cells that expose autoantigens in predisposed individuals might drive autoimmune-mediated tissue injury (see, e.g., Voulgarelis et al, 2010m Nat Rev Rheumatol 6, 529-537; Xanthou et al, 1999, Clin Exp Immunol 118, 154-163) Immune activation is typically presented as focal, mononuclear (T, B and macrophage) cell infiltrates proximal to the ductal epithelial cells (epithelitis) and forms sialadenitis (see, e.g., Voulgarelis et al., ibid.). Though the pathogenetic mechanism for this autoimmune exocrinopathy has not been fully elucidated, it has been shown that CD4+T-lymphocytes constitute 60-70 percent of the mononuclear cells infiltrating the glands (see, e.g., Skopouli et al., 1991, J Rheumatol 18, 210-214). Abnormal activation of proinflammatory Th1 (see, e.g., Bombardierei et al., 2004, Arthritis Res Ther 6, R447-R456; Vosters et al., 2009, Arthritis Rheum 60, 3633-3641) and Th17 (see, e.g., Nguyen et al., 2008, Arthritis and Rheumatism 58, 734-743) cells have been reported to be central to induction of SS in either human or animal models.
Activation of Th1 and Th17 cells is initiated by antigen presentation, which requires the engagement not only of the T-cell receptor (TCR) to MHC molecules from antigen presenting cells (APCs), but also appropriate costimulatory signaling (see, e.g., Smith-Garvin et al., 2009, Ann Rev Immunol 27, 591-619). One of the crucial pathways of costimulation is the interaction of CD28 on the T cell with B7.1 (CD80)/B7.2 (CD86) on antigen presenting cells. Cytotoxic T-lymphocyte antigen 4 (CTLA-4; also referred to as CD152) displays a wide range of activities in immune tolerance. The main function of CTLA-4 is to bind to B7 and compete for its interaction with CD28, thereby shutting down the B7:CD28 pathway and subsequently initiating the deactivation of the T cell response and maintaining immune homostasis (see, e.g., Perkins et al., 1996, J Immunol 156, 4154-4159). Moreover, CTLA-4 is constitutively expressed on CD4+CD25+Foxp3+ natural regulatory T cells (nTreg), which play a crucial role in immune tolerance and ultimately protection from autoimmune disease (see, e.g., Sakaguchi et al., 2006, Immunological Reviews 212, 8-27). CTLA-4 is required by nTreg cells for suppressing the immune responses by affecting the potency of APCs to activate effective T cells (see, e.g., Wing et al., 2008, Science 322, 271-275; Takahashi et al., 2000, J Exp Med 192, 303-310). It is known that T cell autoimmunity is controlled by the balances between Th17/Treg cells (see, e.g., Eisenstein et al., 2009, Pediatric Research 65, 26R-31R) and Th1/Th2 cells (see, e.g., Nicholson et al., 1996, Current Opinion Immunol 8, 837-842). Thus, CTLA-4 could represent an important therapeutic target, shifting the T cell balance from proinflammatory T17 and/or Th1 towards suppressing Treg and/or Th2 cells. Other immunological manifestations of Sjögren's syndrome include the formation of auto-reactive antibodies such as anti-nuclear antibodies (ANA), SSA antibodies (e.g., SSA/Ro), SSB antibodies (e.g., SSB/La), and M3R antibodies.
While some treatments that have proven effective for certain autoimmune diseases, such as rheumatoid arthritis, currently there are no effective therapies for the treatment of Sjögren's syndrome. For example, anti-tumor necrosis factor (TNF) agents have been shown to have beneficial effects in the treatment of rheumatoid arthritis as well as in other inflammatory arthritides and diseases. Etanercept (ENBREL™), a fusion protein of soluble TNF receptor 2 and the Fc region of immunoglobulin IgG1, is marketed for a number of such conditions. However, Etanercept has been shown to be ineffective in a clinical trial of patients with Sjögren's syndrome (see, e.g., Moutsopoulos et al., 2008, Ann Rheum Dis 67, 1437-1443). In addition, administration of an AAV vector encoding soluble TNF receptor 1-Fc fusion protein to the salivary glands of a murine model of Sjögren's syndrome has been shown to have a negative effect on salivary gland function (see, e.g., Vosters et al., 2009, Arthritis Res Ther 11, R189).
As discussed above, one hallmark of Sjögren's syndrome is xerostomia (dry mouth), resulting from immune system-mediated destruction of the salivary glands and the consequent loss of the ability to produce saliva. Aquaporin-1 (AQP-1; formerly known as CHIP28) is a 28-kilodalton protein present in renal tubules and erythrocytes, which has similarity to other membrane channels proteins (see, e.g., Preston and Agre, 1991, PNAS 88, pp 11110-11114). AQP-1 is plasma membrane protein that forms channels in the membrane, thus facilitating rapid transmembrane water movement in response to an osmotic gradient. Although members of this family generally show only about 30% identity, several features are preserved. For example, the overall size of each subunit is approximately 30 kDa. Furthermore, hydropathy analyses of these proteins are similar, suggesting six transmembrane helices and having two Asn-Pro-Ala signature motifs (or close variants). A detailed structural analysis of AQP-1 has been described by Heymann et al., Journal of Structural Biology 121, 191-206 (1998), which is incorporated by reference, herein in its entirety. Similarly, a family of aquaporin proteins have been identified, including AQP-2, AQP-3, AQP-4, AQP-5, AQP-6, AQP-7, AQP-8, AQP-9, AQP-10, and AQP-11,
Previous work has attempted to use virus-mediated transfer of a gene encoding AQP-1 to restore fluid secretion in the parotid glands of miniature pigs that had been irradiated to destroy parotid gland function (see, e.g., Gao et al., 2011, Gene Therapy, 18, pp 38-42). However, there are no reports of anyone trying to restore salivary flow in patients suffering from Sjögren's syndrome as the cause of the xerostomia in this disease is thought to be immune related such as auto antibodies or proinflammatory cytokines.
Thus, there remains a need for an effective composition to protect subjects from, and treat subjects for, xerostomia associated with Sjögren's syndrome.